This application claims priority to Japanese Patent Application No. P2000-357616.
1. Field of the Invention
The present invention relates to an information storage system including a magnetic head and a magnetic recording medium and, more particularly, relates to a portable magnetic hard disk drive having an improved shock resistance performance particularly during operation.
2. Description of the Background
The magnetic hard disk used in current magnetic hard disk drives typically includes a structure in which servo areas and data areas divided into a plurality of sector blocks are formed on concentrically formed tracks as shown in FIG. 6. In each of the servo areas, a specific bit pattern referred to as a servo pattern is recorded. Accurate information about the positioning of the magnetic head is performed by obtaining a head position signal from the servo pattern. The servo pattern typically includes an ISG (Initial Signal Gain) field, an SVAM (Servo Address Mark) field, a Gray code field, a burst field, a padding field, and other information as generally shown in FIG. 7.
When an external shock is applied to a magnetic hard disk drive during a recording operation of a magnetic head, the magnetic head may be displaced in the direction of track width. When this displacement occurs, the recording operation is preferably aborted so that adjacent tracks are not overwritten. In JP-A-97770/1998, there is disclosed a technology where a parity bit is provided at the boundary between adjacent tracks in a servo area in order to detect in which direction a head has moved (either an inward or outward radial direction of the disk) upon the occurrence of a positional displacement of the head. Further, for a compact magnetic hard disk drive, there may be a continuous monitoring for an external shock in which the compact magnetic hard disk drive further includes an acceleration sensor as described below.
A magnetic head typically obtains position information by detecting a head position signal from a servo area while moving over a track. However, only about from 50 to 100 servo areas are provided per circumference of a disk. Therefore, only a minimal amount of servo information can be obtained. Accordingly, even if a positional displacement of the head occurs between servo areas, the head may not accurately detect the occurrence of the positional displacement thereof.
FIGS. 9(a) to 9(c) illustrate a manner in which the adjacent track is destroyed due to the positional displacement of the head. FIG. 9(a) shows the state in which the recording operation has been normally performed. On the other hand, FIGS. 9(b) and 9(c) show two examples of a state in which the data of the adjacent track is destroyed due to the positional displacement of the head. The cross-hatched region denotes the track (#2) to which the recording operation has been performed.
Referring now to FIG. 9(b), the positional displacement of the head occurs during the recording operation on the data area (sector block #2), and the movement of the head is detected at the next servo area (#2). Upon this detection, the recording operation is preferably aborted. However, the head has already moved well into the undetectable section, and the data in the data area (sector block #4) of the adjacent track (#3) has been overwritten and corrupted.
FIG. 9(c) shows a state in which the recording operation has been performed at the position extending across a boundary between the adjacent tracks to form a data sector extending across a boundary between the track (#2) and the track (#3). In the state of FIG. 9(c), even if the data can be normally reproduced, a user may not be able to distinguish which data is the proper data written in final update. Hence, incorrect or unreliable information may exist in sector (#4) of tracks (#2) and (#3).
The number of servo areas per circumference of a disk may be increased in order to reduce the interval at which the head position is detected (thereby decreasing the time it takes to detect a position fault). However, the size of the data areas will undesirably decrease with the number of servo areas increases.
Further, in some applications an acceleration sensor has been employed to detect and compensate for positional errors in a hard disk drive. However, it may be difficult to estimate the relative positions of the head and the disk from the acceleration sensor when continuous vibrations or similar disturbances are applied to the disk.
For at least the reasons described above, the function of detecting the positional displacement of the head of a conventional magnetic hard disk drive does not have the desired accuracy such that the recording operation can be reliably aborted upon the occurrence of positional displacement. Under such circumstances, particularly for a magnetic hard disk drive with an increased data track density, a need may exist to provide a technology in which the shock resistance performance during operation is improved by preventing the fatal error of overwriting of the adjacent tracks to enhance the reliability of the disk.
In a magnetic hard disk drive according to at least one preferred embodiment of the present invention, an area in which track position information having a smaller data size than that of the recorded servo information is provided immediately at the front of each sector block in order to address one or more of the foregoing limitations of the conventional magnetic disks. In the present invention, the area in which track position information having a smaller data size than that of servo information is recorded is referred to as a xe2x80x9cmicro-servo area.xe2x80x9d The track position information preferably has a smaller data size than that of the servo information so as not to require a compression in the data area.
The micro-servo area may also be formed with a smaller area than that of the servo area. In preferred embodiments, the track position information recorded in the micro-servo area are set to be mutually different at least between adjacent tracks. The track position information may include, for example, a parity code indicating whether the track number is odd or even. Consequently, even if a positional displacement of the head occurs between the servo areas, the magnetic head can preferably recognize that it has moved over a different track from the adjacent track.
With the technology disclosed in the JP-A-97770/1998, for example, since the parity bit is formed in a servo area, it may not be possible to know the position information between the servo areas. Therefore, with the technology disclosed in the JP-A-97770/1998, it may not be possible to reliably generate a write halt signal in high speed, high density application using the conventional techniques.
In the micro-servo area, besides for the track parity information, information for ensuring the recognition of being the micro-servo area is also preferably recorded. For example, the same signal pattern as the address mark in the servo area may be recorded. However, a different signal pattern from the servo address mark field in the servo area is preferably recorded in the address mark field in the micro-servo area in order to avoid confusion between these two areas.
Further, with the magnetic hard disk drive of the present invention, prior to the write operation to the target sector block, the corresponding track position information is preferably checked. Then, whether the recording operation to the target sector block is permitted or aborted is determined. At this step, if the recording operation is aborted, a retry operation and the determination by check of the track position information are repeated.
Alternatively or additionally, an acceleration sensor may be provided therein, so that the recording operation to the target sector block is permitted only if both the condition that the output value from the acceleration sensor is smaller than a prescribed value and the condition for determination of the track position information are satisfied.
These and other objects, features and advantages of at least some embodiments of the present invention will appear more fully from the following detailed description of the invention, the drawings, and the attached claims.